--- title: "GNU Privacy Guard: Crypto Cheatsheet" date: 2026-03-19 updated: 2026-03-19 author: [The Tech Prepper] categories: [cryptography] tags: [gpg, pgp] copyright: "(C) 2026 The Tech Prepper, LLC" --- This is an in-progress cheatsheet for performing basic cryptographic functions using GNU Privacy Guard (gpg), including encrypting, decrypting, and verifying files in an offline environment. ## Add Key Import a public key into your keyring. 1. Download the public key from the trusted individual. It can be saved anywhere. For ease of backup, save it under `~/keys/`. Create this directory if it does not exist in your home directory. 2. Import the key file. gpg --import KEYFILE 3. Verify the key fingerprint. Your trusted source should provide you with the fingerprint. From the example above, the fingerprint is the value starting with `77F8`. gpg --fingerprint 4. Optionally, edit the key and set the trust level. See the "Set Trust Levels" section. 5. For an off-grid use case, where you trust the key, you can sign it yourself to mark the key valid on your machine. gpg --lsign-key FINGERPRINT Here's an example from EmComm Tools Community R6 that imports the AmRRON public key. ``` $ gpg --import ~/Desktop/offline/nets/amrron/AmRRON_Actual_ECC_PUBLIC.asc ``` ## List Public Keys List the current public keys on your system. ``` gpg --list-keys ``` Use the following to interpret the keys listed: - `pub` - Primary key - Your identity - Used for signing and certifying other keys - `sub` - Subkey - Used for specific operations (usually encryption) - Can be replaced or rotated without changing identity - Can be revoked or rotated if compromised - `[SC]` - Sign + Certify - `[E]` - Encrypt - `unknown|full|ultimate` - See "Set Trust Levels" Here's an example showing the AmRRON public key. ``` $ gpg --list-keys /home/ham/.gnupg/pubring.kbx ------------------------------- pub ed25519 2023-05-25 [SC] 77F888F3524F00C75FF9F91A8D518D7A50612239 uid [ unknown] AmRRON Actual (ECC) sub cv25519 2023-05-25 [E] ``` ## Verify Signature There are two common types of signed files: ### 1. Embedded Signature A single file that contains both the message and the signature. For example, the AmRRON Intelligence Brief (AIB) uses an inline message. gpg --verify COMBINEDFILE ### 2. Detached Signature A file and a separate signature file. gpg --verify SIGNATUREFILE FILE Here's an example from EmComm Tools Community R6 that verifies that the AIB distributed by AmRRON on the nationwide net on March 16, 2026 was created by AmRRON. ``` $ gpg --verify ~/Desktop/offline/nets/amrron/NATL-RR-260316-1330Z-AIB-sig.k2s gpg: Signature made Mon 16 Mar 2026 06:22:46 AM MST gpg: using EDDSA key 77F888F3524F00C75FF9F91A8D518D7A50612239 gpg: checking the trustdb gpg: marginals needed: 3 completes needed: 1 trust model: pgp gpg: depth: 0 valid: 1 signed: 1 trust: 0-, 0q, 0n, 0m, 0f, 1u gpg: depth: 1 valid: 1 signed: 0 trust: 0-, 0q, 0n, 0m, 1f, 0u gpg: Good signature from "AmRRON Actual (ECC) " [full] ``` ## Create Key Generate a new private/public key pair using ECC. It is a modern standard that provides strong security and works well for radio use due to smaller key sizes. 1. Create a primary key for signing using ECC. Replace FIRSTNAME, LASTNAME, and EMAIL. NOTE: You MUST keep `<` and `>` characters around your EMAIL. For example: `John Doe `. gpg --quick-generate-key "FIRSTNAME LASTNAME " ed25519 sign 0 2. List your keys and identify the fingerprint of your new key. gpg --list-keys 3. Generate an encryption subkey. Replace FINGERPRINT. gpg --quick-add-key FINGERPRINT cv25519 encrypt 0 4. List your keys again. You should now see a subkey that is suitable for encryption (`[E]`). gpg --list-keys ## List Private Keys List the current private keys on your system. ``` gpg --list-secret-keys ``` ## Sign File Signing a file allows recipients to verify the sender is authentic and that the file has not been modified in transit. Create a test file: echo "This is a test file for gpg training." > file.txt There are two common ways to sign a file. ### Embedded Signature Create a single text file that contains both the message and the signature. gpg --clearsign file.txt This creates: file.txt.asc ### Detached Signature Create a separate ASCII signature file for the original file. gpg --armor --detach-sign file.txt ## Encrypt / Decrypt File Encryption protects a file so that only the intended recipient can read it. Decryption restores the original file using your private key. Create a test file: echo "This is a test file for gpg training." > file.txt ### Encrypt File Encrypt a file for a specific recipient. Replace RECIPIENT with the recipient email or key ID. This command also signs it (`-s`) and encrypts the output as plain ASCII (`--armor`). gpg --armor -e -s -r RECIPIENT file.txt This creates: file.txt.asc ### Decrypt File Decrypt a file that was encrypted to you. gpg -d file.txt.asc > decrypted.txt This creates: decrypted.txt ## Set Trust Levels Here are common trust levels for basic use: - `unknown` - No trust assigned (default) - `full` - You trust this person to sign other keys - `ultimate` - Your own key Perform the following steps to change the trust level for a key. 1. List the keys and identify the key ID (KEYID). gpg --list-keys 2. Replace `KEYID` with the key ID to edit. gpg --edit-key KEYID 3. Type `trust` and press [ENTER]. 4. Type the number for the desired trust level and press [ENTER]. 5. Type `quit` to exit. ## Export Keys If you need to back up your keys, export them as follows. ### Export Public Key To export your public key for distribution, run the command below. Replace EMAIL with the email address attached to the key. This file can be shared with your community. gpg --export -a EMAIL > public.asc ### Export Private Key WARNING: DO NOT SHARE THIS KEY WITH ANYONE. gpg --export-secret-keys -a EMAIL > private.asc Restrict permissions to read-only for your user: chmod 400 private.asc Store this file securely and be careful when moving it between systems.